Conventional variable pitch propellers have a hub and separate blades, the blades having circular cross sections at the root so that the blades pivot on bearings for pitch change. High centrifugal force requires a strong and heavy hub and bearings. Making matters worse, the circular root cross section results in high out-of-plane stiffness, so that gyroscopic loads and any unbalance between centrifugal force and thrust causes a bending moment around the hub-blade intersection, causing a stress that adds to centrifugal force-induced stress. The circular root cross section also results in drag but no thrust, reducing propeller efficiency.
A flexible beam design has been applied to helicopter main rotors (e.g. U.S. Pat. No. 4,332,525), helicopter tail rotors (e.g. U.S. Pat. No. 4,381,902), and wind turbines (e.g. U.S. Pat. No. 4,522,564), but the prior art does not disclose solutions to the problems experienced in application to aircraft propellers.